Remove useless OOM handling

[silvioprog]

Hello,

there are some points which handles OOM in a pessimist way, for example: src/sg_httpres.c#L153.

Such handling should be replaced by something like this:

...
    if (!(res->handle = MHD_create_response_from_buffer(size, buf, MHD_RESPMEM_MUST_COPY)))
        return ENOMEM;
...

so the programmer has a chance to decide how the OOM will be handled at run time. (it is already possible at build time by replacing the oom() macro too)